The present invention relates to a printer, or a fixing device used for image forming devices such as copying machines, facsimiles and printers.
Demands for faster and more energy-efficient image forming devices such as printers, copying machines and facsimiles have been increasing in the market. To satisfy such demands, it is critical to improve the thermal efficiency of fixing devices used in the image forming devices.
During image forming processes such as electro-photographic recording, electrostatic recording and magnetic recording, an image forming device forms an unfixed toner image on recording media such as recording sheets, photosensitive paper and electrostatic recording paper by an image transfer method or a direct method. The unfixed toner image is fixed, in general, by a fixing device based on contact heating methods such as a hot roller method, a film heating method, or an electromagnetic induction heating method.
The fixing device of the hot roller method comprises, as a basic construction, a pair of rollers including a temperature regulated fixing roller having a heat source such as a halogen lamp and a press roller pressing against the fixing roller. A recording medium is inserted into and carried through a section where the fixing roller and press roller come into contact, a so-called fixing nip portion, so that the unfixed toner image is melted and fixed by heat and pressure applied by the rollers.
The fixing device of the film heating method is disclosed, for example, in the Japanese Patent Laid-Open Publications S63-313182 and H01-263679.
In the case of the foregoing fixing device, a recording medium is positioned into a close contact with a heater which is tightly fixed to a supporting member via a thin heat-resistant fixing film. The fixing film is slid against the heating body and the heat is transferred from the heating body to the recording medium via the film.
International Publication WO 00/52534 A1 discloses a fixing device based on the electromagnetic induction heating method. According to the method, Joule heat produced by an eddy current generated in a magnetic metal member by an alternating field heats up a heater, including the metal members, by an electromagnetic induction. A heating roller is heated by electromagnetic induction heating, and the heat is transferred to a thin heating medium made of a heat-resistant resin by thermal conduction.
The present invention aims to provide a printer in which a stable temperature for fixing a toner image can be maintained stable.
The printer of the present invention comprises an exposure device for generating a light beam corresponding to an image information, a photosensitive body on which a latent image is formed based on the light beam delivered from the exposure means, a charger for charging the photosensitive body, a developer for converting the latent image formed on the photosensitive body into a visible image using toner particles, a belt on which the visible toner image is transferred, and a fixing device for fixing the toner image on the belt onto a recording medium.
The foregoing fixing device comprises a heating roller containing a magnetic metal, a fixing roller disposed parallel to the heating roller, an endless belt bridging the heating roller and the fixing roller, a press roller pressed to the fixing roller via the endless belt and recording medium, and a device for producing magnetic fields disposed adjacent to the heating roller.
The endless belt contains magnetic metal or the belt is made of materials that can be heated by magnetic induction heating. The device for producing magnetic fields causes both of the heating roller and the endless belt to generate heat.